Previous work in this laboratory has demonstrated that SC cells are homogeneously denser than SS cells (increased MCHC); they have evidence of HbC driven crystallization, special morphology and hyperdense reticulocytes. In addition the expression of HbF is variable among African-American (between 1-8%) while it is invariably low (less 2%) in Center West Africans with the same genotype. In this proposal we will study the haplotype (both C and S linked) effect on clinical expression and HbF levels as well as the effect of alpha-thalassemia on the hematological parameters, particularly presence of SC cells containing crystals. Since there is very little understanding on red cell volume regulation on SC cells, we will bring to bear our experience in the field in collaboration with the laboratory of Mitzy Canessa at Brigham and Womens. First, we need to describe the presence and activity of volume-regulating transporters in different density-defined cell fractions as well as understand the effect of deoxygenation on these ion transport mechanisms. The third aspect of the project also stems from previous work done in this laboratory. We are interested in testing the hypothesis that crystal-containing SC cells do NOT vasocclude because the crystal melts when deoxygenated. We will pursue the successful approach of defining the residues of contact in the modulation of the rate of HbC driven- crystal formation as well as the relationship between HbC and the cytoskeleton membrane (cytosolic portion of Band 3 primarily) both as a potential nidus of crystallization as well as of functional-modified hemoglobin molecules. This project brings together diverse in-house and proven outside collaborators for a comprehensive investigation of the pathobiology of SC disease. The fact that red cell volume regulation is the center piece of the abnormality, exploring ways to relieve the reduction of volume could lead to a cure of the disease, on a track that is different from and not directly applicable to SS disease.